There was no information on what food or medical aid the Red Crescent workers were able to take with them. The ICRC has been waiting for permission from Syrian authorities to enter Baba Amr since last Friday.

Syrian authorities had said access was being denied because of safety concerns over mines and unexploded bombs, but the opposition charges that the delay is aimed at allowing time for the regime's "crimes" to be covered up.

Baroness Amos flew in for a two-day visit after an international outcry over President Bashar al-Assad's previous refusal to let her in, and she is to followed by UN-Arab League envoy Kofi Annan on Saturday.

Walid Muallem, the foreign minister, said in talks with Amos soon after she arrived in Damascus that Syria was ready to co-operate with the UN humanitarian delegation.

The state SANA news agency said Mr Muallem "underlined Syria's commitment to co-operate with the delegation within the framework of the respect, sovereignty and independence of Syria."

It quoted Mr Muallem as saying Syria was doing its best to provide food and medical assistance to its citizens despite "the burden it faces as a result of unfair sanctions imposed by some Western and Arab nations which are affecting the population."

Baroness Amos's arrival coincided with a report by the Syrian National Council, the main opposition grouping, that army reinforcements were on their way to Idlib province, a stronghold of Turkey-based Free Syrian Army rebels.

"The SNC has noted 42 tanks and 131 troop carriers leaving Latakia in the direction of the town of Saraqeb," in Idlib, "as well as military columns heading for the town of Idlib," the group said in a statement.

In addition, "several martyrs were killed" in bombardment of Maaret al-Numan, another town in Idlib province, it added.

The SNC called on the international community, the Arab League and international NGOs to "act urgently and at all levels, to avoid a repeat of the massacre at Baba Amr, where hundreds of martyrs fell."

The group urged rebel fighters in the Damascus, Aleppo and Hama regions to "take all the necessary initiatives to alleviate the pressure on our brothers in Idlib."

Baba Amr, a rebel district in the flashpoint city of Homs, was overrun last Thursday after almost a month of shelling by Syrian forces that cost hundreds of lives and which the SNC said reduced much of the city to rubble.

The Syrian army has intensified its attacks on insurgency strongholds, particularly in Idlib, since it retook Baba Amr.

Also on Wednesday, a Chinese envoy sent to discuss ways to end the bloodshed in Syria was to discuss a six-point peace plan with Muallem and opposition figures.

The Chinese initiative calls for an immediate end to the violence and for dialogue between Assad's regime and the opposition.

Beijing's proposal rejects foreign interference or "external action for regime change" in Syria but supports the role of the UN Security Council "in strict accordance with the purposes and principles of the UN charter."

Russia, which like China has been criticised for blocking Security Council action on the crisis, urged its ally Damascus and the rebels to "immediately" halt violence and assist Amos's mission.

The Russian foreign ministry said it received Syria's ambassador to Moscow at his own request and made clear that "violence must end immediately, no matter where it comes from."

Russia also "underscored the critical need to solve acute humanitarian problems in Syria," the ministry said.